i tried googling it too, and the results are mixed. some say it doesn't matter, some say to toss it out.
however the problem seems to be simply that it's less effective, so there would be no harm in trying.
from the official aspirin website:
Can I still use Aspirin® after the expiration date?
No, it is not recommended to use any over-the-counter product beyond the labeled expiration date. Like all drugs, Aspirin® can deteriorate over time and not be as effective. Be sure to check the package for the expiration date.
Read the package insert and directions for use before using Aspirin®. For further information on benefits, risks and side effects please consult your physician or pharmacist!